This invention relates generally to an air-natural gas carburetor of the type that are used to mix air and gaseous fuel such as CNG (natural gas); and, more particularly, to a stationary engine application on an irrigation well with a constant load which supplies a rotary walking sprinkler. The air and gas valves controlling the air/fuel ratio of the fuel charge are separately manually controlled.
Mixing devices generally referred to as carburetors, for mixing air with a gaseous fuel, are well known in the prior art and such devices are commonly attached to the intake manifold of an internal combustion piston engine in lieu of a conventional liquid fuel carburetor, which would normally operate the engine. In the operation of such carburetors, also referred to as air/gas carburetors, the mixing of air and gaseous fuels needs to be in a generally proper ratio for a particular engine load and speed. In the gaseous fuel carburetors currently on the market, the amount of air and the amount of fuel are controlled by valves that are positioned by the engine manifold pressure. The air and gas valves within these prior art carburetors typically are tied together so that at various throttle settings, the mixture of the air/fuel charge remains relatively uniform.
The present invention deviates from this conventional approach in that the air-flow valve and the fuel-flow valve are independently manually controlled which is a concept not followed in carburetor design.
In a typical prior art air/gaseous fuel carburetor, shown in U.S. Pat. No. 3,545,948, the gas valve is actuated by use of a diaphragm operated by vacuum pressure from the engine which is sensed from the intake manifold. The diaphragm opens the gas valve in response to vacuum manifold pressure and the degree of the valve opening is controlled by manifold pressure. Since the air and gas valves move together the air/fuel mixture at any given manifold pressure is relatively uniform.
In a later air/gas carburetor, shown in U.S. Pat. No. 4,694,811, the air and fuel valves also move together subject to manifold pressure but also include a stepper motor that adjusts the fuel valve alone to vary the fuel/air mixture. This design is intended to deal with the differing b.t.u. content of the gaseous fuel which requires adjustments to the fuel/air mixture ratio for any given engine load when the fuel is changed.
In more recent air/gas carburetors, such as U.S. Pat. No. 5,809,970, the control is completely automatic with the use of mass flow rate sensors which sense the mass flow rate of both the aspirated air and injected fuel, and generate a control signal for each fuel and air valve to maintain the optimum stoichiometric ratio for the air and natural gas which adjusts at every change in throttle position of the engine.
All current gaseous fuel carburetors on the market utilize manifold pressure as a power source to adjust the air and gaseous fuel valves and rates of flow found in the carburetor. The present invention utilizes manual adjustment of both the air and gaseous fuel valves separately to obtain a minimum of fuel usage with the leanest fuel-air ratio.
The carburetor of the present invention is utilized on internal combustion reciprocating piston engines which operate at a constant load while driving turbine type irrigation pumps. These irrigation pumps operate at a constant rpm and have an unchanging load for each location since the lift of the pump or head is constant along with the pressure to move the water through the irrigation sprinkler system. These pumps are also used for a flood irrigation system. Contrary to most power supply systems, the pumps operated by the present invention have a constant load and there is no requirement for changing the air valve or gas valve settings other than the start up and the shut down of the pump, which is achieved by closing the gas valve.
The primary object of the present invention is to provide air-natural gas carburetor that operates with a minimum amount of fuel for each gallon of water pumped.
Another object of the present invention is to provide a simplified carburetor design which entails merely two manually controlled valves and a downstream gas pressure regulator without any of the automatic controls normally utilized in current air-gaseous fuel carburetors on the market.
Another object of the present invention is to provide instrumentation with the carburetor to achieve an optimum air-fuel ratio.
A further object of the present invention is to provide an air-gaseous fuel carburetor that is economical to manufacture and to run relatively maintenance free.